1. Field of the Invention
This invention relates to a motor structure in a salient pole type DC motor in which a cogging torque and a torque ripple are reduced without decreasing an efficiency, a torque constant and hence the irregularity of rotation is reduced.
2. Description of the Prior Art
Heretofore, as a method for reducing the irregularity of a torque or rotation, there has been a type of motor in which switching is conducted in a (2n+1) phase, the ratio of the number of the poles of a rotor magnet to the number of salient poles wound with the winding of a stator core is (2n+2):(2n+1), and the phase currents of the stator windings are sequentially switched in response to the rotating position, as for example, disclosed in Japanese Patent Publication laid-open No. 49-8568. In this type, the number of cogging torque becomes the least common multiple of the number of the stator windings and the number of the poles of the rotor magnet, the number of the cogging torque per one revolution is increased, the apparent value is felt to be small, but does not become "0". Accordingly, in the case of a motor which is used at a low speed so that the irregularity of its rotation becomes a problem like, for example, a record player turntable drive motor or a floppy disk spindle motor, a method of providing an interpole at the stator, a slot pitch is formed to be not uniform but irregular or the shape of a salient pole piece is altered are used together.
However, although these methods can reduce the irregularity of the torque but, have disadvantages that the motor efficiency and the torque constant are also decreased.
On the other hand, as to the method of forming grooves or slits on a rotor magnet, there is a method described in "Brushless DC motor and rotor magnet thereof" of Japanese Patent Application laid-open No. 1-318536 filed by the same inventors as this application. This prior invention is a motor comprising:
1) a stator having salient poles wound with windings and interpoles wound without windings, PA0 2) the number of rotor pole detecting means applied to a brushless DC motor being one, and PA0 3) the number of grooves or slits being half the number of the poles. PA0 1) the starting torque is stabilized, and PA0 2) the motor efficiency is improved.
This prior invention has features that
The prior invention is fundamentally different from the present invention.